The invention relates to a cleaning system for cylinder surfaces of a printing machine. Accordingly, the present cleaning system comprises a number of automated cleaning devices are each allocated to one or more cylinders. The cleaning devices are each provided with a supply line for feeding a detergent. The supply lines receive the detergents from a common feed pipe, with at least one pump being allocated to the feeding device, in general.
Printing machines, and here in particular newspaper rotary printing machines, high-speed jobbing machines, and sheet-fed letterpress printing machines of all types of printing methods, such as offset printing, anilox printing, intaglio printing, flexo printing, anilox-flex high and low printing are addressed. All drums, rollers, and cylinders of a printing machine are included under “cylinders”, whose surfaces are to be cleaned, in particular rubber blanket cylinders, grounding-in cylinders, plate and form cylinders, cooling cylinders, guiding rollers, as well as color cylinders.
All printing machines mentioned have in common that for guidance, processing, and drive of sheets or webs to be printed an intense contact is required between the material to be printed and the cylinders. Here, residue of paper dust (fibers, coat, fillers, etc.), ink, and perhaps powder dust develops, for example when paper is used as the material to be printed. This residue interferes with the functionality of the cylinder. For example, residue in rubber blankets in offset printing leads to the loss of dot sharpness in the print and some printing sections do not print correctly. For maintaining printing quality as well as operational safety, it is mandatory that the above-mentioned cylinders are regularly cleared of contaminants.
This generally occurs via automatic cleaning devices, which apply detergents onto the cylinder surfaces to be cleaned and use brushes or cloth, if necessary, in order to lift the contaminants partially dissolved by the detergent off the cylinder surface. An example for one such cleaning device is described in EP 1 106 355 A1.
In high-speed jobbing machines ink is used, which needs to be dehydrated after printing, so that the respective printing machines are provided with a dryer, through which the printed material is guided after the printing process. The dehydration occurs at elevated temperatures, so that safety aspects come to the fore: the ink contains evaporating hydrocarbon—components, which can reach a flammable concentration in the dryer under unfavorable conditions. Accordingly, the heat influence in the dryer as well as the production speed, which is influential on the time the printed material remains between the printing process and the drying process, is to be adjusted such that the concentration of hydrocarbons in the dryer always remains below a limit, i.e. below 25% of the lower explosion limit.
In order to avoid considerable production stops the regularly necessary cleaning of the cylinder surface of the printing machine must be performed under production conditions when printing paper webs, i.e. the cylinders to be cleaned are in contact with the paper web during the cleaning process. Therefore, during the cleaning process the paper web transports detergent into the dryer. However, the commonly used detergents have a relatively high portion of evaporating hydrocarbons, so that here too it must be ensured that the concentration of hydrocarbons in the dryer does not become too high. Therefore, too much detergent must not be used in the cleaning process.
In particular in web offset printing machines for high-speed jobbing material of a high value is used. From 10 to 30 spoiled copies per second develop during the cleaning process at production speed. Therefore, for reasons of cost, the cleaning process is to be kept as short as possible. However, that requires that relatively large amount of detergent must be used, because the effective time, in which the detergent dissolves the contaminants, is very limited.
Therefore, there are two contradicting objectives: on the one hand, the amount of detergent used for cleaning is to be kept as small as possible, because otherwise too much hydrocarbon—containing detergent enters the dryer and causes the risk of the concentration of hydrocarbons becoming too high. On the other hand, the time for the cleaning process shall be kept as short as possible. Therefore, the use of the detergent is to be optimized such that a cleaning effect is achieved as good as possible, with a duration of the cleaning process being kept as short as possible with the use of as little detergent as possible.
Controlling the application of the detergent during the cleaning process is more expensive by such an optimization. The more it is mandatory to ensure a trouble free and absolutely reliable control of the amount of detergent used, in order to prevent that accidentally too much detergent is carried along by the printed material web into the dryer and an excessively high hydrocarbon concentration develops, here.